Radiation detector, scintillator panel, and methods for manufacturing same

ABSTRACT

An image sensor panel ( 2 ) has a light receiving section ( 22 ) consisting of a plurality of photoelectric detectors ( 21 ) two-dimensionally arranged close to corners on a substrate ( 20 ). The image sensor panel ( 2 ) has a scintillator ( 3 ) formed successively from the surface of the light receiving section ( 22 ) to sidewall parts ( 25 ) close thereto. A screen is enlarged by butting the sidewall parts ( 25 ) against each other.

TECHNICAL FIELD

This invention relates to a radiation detector and a scintillator panel,and, more particularly, to a radiation detector and a scintillator panelthat can be suitably applied to a radiation imaging device constructedby arranging a plurality of image sensors so as to pick up a radiationimage having a large image area, and to methods for manufacturing them.

BACKGROUND ART

An X-ray image sensor using a CCD, in place of an X-ray photosensitivefilm, has been widely employed as an X-ray diagnostic instrument formedical use. In such a radiation imaging system, two-dimensional imagedata by radiation is obtained as an electrical signal by use of aradiation detector that has a plurality of pixels, and an X-ray image isdisplayed on a monitor by processing the signal with a processor. Atypical radiation detector has a mechanism in which a scintillator isdisposed on photodetectors arranged one-dimensionally ortwo-dimensionally, and incident radiations are transformed by thescintillator into light in a wavelength region to be sensed by thephotodetectors, and are detected.

In this type of radiation detector, a yield obtained when manufactureddeteriorates proportionately with the enlargement of an image. As asolution to this problem, a technique is known in which a plurality ofdetectors are arranged to enlarge an image when a large-screen imagingdevice for use in taking a chest X ray, for example, is produced, asdisclosed in JP 09-153606 A. This publication mentions that the yield ofeach component is prevented from decreasing, and production costs arereduced by combining the components of a light receiving screen smallerthan an actual imaging screen together.

DISCLOSURE OF THE INVENTION

However, there is a problem that a scintillator is liable to separatefrom a boundary (a joint) with an adjoining detector when a plurality ofdetectors are arranged to make a large screen in this way. This problemcauses a concern that the resolution in the vicinity of the joint willdecrease or that the scintillator will completely separate therefrom.

It is therefore an object of the present invention to provide aradiation detector and a scintillator panel that are constructed so thatresolution in the vicinity of a joint can be prevented from decreasing,and the scintillator can be prevented from separating therefrom when aplurality of detectors are arranged for large-area photography, and toprovide methods for manufacturing them.

In order to achieve the object, he radiation detector according to thepresent invention is characterized by comprising (1) an image sensorpanel having a substrate and a light receiving section consisting of aplurality of photoelectric detectors arranged two-dimensionally in thevicinity of at least one side of the substrate, and (2) a scintillatorsuccessively extending from a surface of the light receiving section ofthe image sensor panel to a sidewall close thereto.

On the other hand, a scintillator panel according to the presentinvention is characterized by comprising (1) a scintillator-formingsubstrate, and (2) a scintillator that successively extends from asidewall of at least one side of the scintillator-forming substrate to apredetermined area of a surface of the scintillator-forming substrate.

Since the scintillator successively extends to the sidewall of thesubstrate (the image sensor panel or the scintillator-formingsubstrate), the scintillator formed on the substrate surface can beuniformly formed close to the sidewall. That is, the almost uniformscintillator spread to the edge of the substrate can be formed.

In the image sensor panels or scintillator-forming substrates obtainedin this way, when the sidewalls where the scintillators are formed aredisposed so as to adjacent these sidewalls and fixed to each other, alarge-screen radiation detector or a scintillator panel for a largescreen can be obtained. According to the present invention, an almostuniform scintillator extending to an edge is formed, and therefore thewidth of an area low in sensibility that arises at a joint can becontrolled to a minimum.

Preferably, the image sensor panel has at least one of a circuit sectionelectrically connected to the photoelectric detectors and a bonding padbetween at least one of the other sides that are not adjacent to thelight receiving section of the image sensor panel and the lightreceiving section thereof. Thereby, the readout line of an electricalsignal can be easily formed.

Preferably, a moisture-proof protective film covering the scintillatoris provided. Thereby, the scintillator can be further effectivelyprevented from peeling off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing an embodiment of the radiation detectoraccording to the present invention, and

FIG. 2 is a sectional view thereof.

FIG. 3 to FIG. 8 are views for explaining a manufacturing process of theradiation detector of FIG. 1 (i.e., manufacturing method of theradiation detector according to the present invention).

FIG. 9 and FIG. 10 are views for explaining a conventionalvapor-deposition-substrate holder.

FIG. 11 and FIG. 12 are sectional views showing a scintillator layerproduced by the vapor-deposition-substrate holder of FIG. 9 and FIG. 10,respectively.

FIG. 13 is a sectional view showing a second embodiment of the radiationdetector according to the present invention.

FIG. 14 and FIG. 15 are plan views, each showing the shape of asolid-state image sensing device used in another embodiment of theradiation detector according to the present invention.

FIG. 16 is a sectional view showing a third embodiment of the radiationdetector according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings. Tofacilitate the comprehension of the explanation, the same referencenumerals denote the same parts, where possible, throughout the drawings,and a repeated explanation will be omitted. Additionally, the size andshape of each component in each drawing are not necessarily the same asthe actual ones, and some components are magnified in size and in shapein order to facilitate the understanding thereof.

FIG. 1 is a plan view showing an embodiment of the radiation detectoraccording to the present invention, and FIG. 2 is a sectional viewthereof. In the radiation detector 100 in this embodiment, foursolid-state image sensing devices 2 a to 2 d that are image sensorpanels are disposed on a ceramic base 1 in 2×2 array.

Each solid-state image sensing device 2 is constructed bytwo-dimensionally disposing photoelectric detectors 21 that perform aphotoelectric conversion on a substrate 20 made of, for example, crystalSi. The photoelectric detectors 21 are formed out of photodiodes (PD) ortransistors. The part where the photoelectric detectors 21 are arrangedis hereinafter referred to as a light receiving section 22. The lightreceiving section 22 is placed close to two sides extending from acorner of the surface of the substrate 20 (i.e., from an intersectioncreated when the solid-state image sensing devices 2 are combinedtogether in FIG. 1). Each photoelectric detector 21 is electricallyconnected by a signal line, not shown, to a corresponding electrode pad23 of a plurality of electrode pads 23 disposed along two adjoiningsides of the solid-state image sensing device 2, i.e., along two sidesopposite to two sides on the side of the aforementioned corner through ashift register 24.

Columnar scintillators 3 a to 3 d that transform incident radiation intolight in a wavelength range to which the photoelectric detector 21 issensitive are each formed on the light receiving section 22 of thesolid-state image sensing device 2. Various materials can be used forthe scintillator 3, and, preferably, Tl-doped CsI that has excellentluminous efficiency is used. The scintillator 3 successively extendsfrom the upper part of the light receiving section 22 of the solid-stateimage sensing device 2 to a sidewall 25 of the substrate 20 of the twosides at the corner to which the light receiving section 22 is close.Therefore, the thickness (position “A”) of the scintillator 3 formed onthe photoelectric detector 21 that is closest to the end of the lightreceiving section 22, i.e., closest to the sidewall 25 is almost thesame as the thickness (position “B”) of the scintillator 3 formed on thephotoelectric detector 21 at the other parts, especially at the centerpart.

Further, a protective film 4, with which the scintillator 3 is covered,which extends from between the electrode pad 23 of each solid-stateimage sensing device 2 and the shift register 24 to the sidewall 25, andwith which the scintillator 3 is sealed up, is formed on eachsolid-state image sensing device 2. The protective film 4 is radiolucentand is impermeable to water vapor, and, for this film, it is preferableto use, for example, a poly-para-xylylene resin (manufactured by ThreeBond Co., Ltd; registered name: Parylene), especiallypoly-para-chloroxylylene (manufactured by the same company; registeredname: Parylene C). A coating film of Parylene has excellent propertiessuitable as the protective film 4, because it is extremely small inpermeability to water vapor and gas, is superior in water repellency andin chemical resistance, is excellent in electric insulation even if itis thin, and is transparent to radiation and visible rays.

The solid-state image sensing devices 2 a to 2 d are disposed on thebase 1 while bringing their corner sides close to the light receivingsection into contact with each other and while butting their sidewalls25 where the scintillator 3 is formed against each other. The portion ofthe butted sidewalls 25 is glued and fixed by being filled with resin 6.Thereby, the light receiving sections 22 of the solid-state imagesensing devices 2 can be disposed as close to each other as possible,and an insensible field where an image cannot be obtained can benarrowed by reducing the gap between the light receiving sections asmuch as possible. The electrode pad 23 is disposed around the lightreceiving section 22.

Next, a process of manufacturing the radiation detector 100, i.e., amethod for manufacturing the radiation detector according to the presentinvention will be described in detail with reference to FIGS. 3 to 8.Four solid-state image sensing devices 2 structured as shown in FIG. 3are first prepared. The solid-state image sensing devices 2 are each setin a vapor-deposition-substrate holder 200. FIGS. 4 and 5 are asectional view and a view from below, respectively, after being set.When set, the solid-state image sensing device 2 is contained andsupported in a containing part 200 b by allowing a projection 200 a ofthe vapor-deposition-substrate holder 200 to support an electrode pad 22provided along two sides thereof as shown in FIG. 4. On the other hand,a notch 200 c is formed on the side of the light receiving section 21 ofthe substrate holder 200 close to the light receiving section 21 of thesolid-state image sensing device 2, and the solid-state image sensingdevice 2 is disposed so that the apex of the sidewall 25 is exposed to avapor-deposition chamber 201.

The vapor-deposition-substrate holder 200 is set in an vapor depositionapparatus in this state, and CsI doped with Tl is grown as columnarcrystals of about 250 μm in thickness on the light receiving section 22of the solid-state image sensing device 2 according to a vacuumdeposition method, so as to form a layer of the scintillator 3 (see FIG.6). Around the light receiving section 22 of the solid-state imagesensing device 2 disposed in the vapor-deposition-substrate holder 200,only the projection 200 a exists as a portion projecting from the lightreceiving section 22 toward the vapor-deposition chamber 201, andtherefore the layer of the scintillator 3 is formed successively towardthe projection 200 a, i.e., up to the sidewall 25 excluding theelectrode pad 23. As a result, it is possible to form a layer of thescintillator 3 almost uniform in thickness extending to the edge part ofthe photoelectric detector 21 close to the sidewall 25.

Since CsI has high hygroscopicity and will be dissolved while absorbingthe water vapor of the air if it remains exposed, the whole of thesolid-state image sensing device 2 where the scintillator 3 is formed iswrapped with 10 μm-thick Parylene according to a CVD (chemical vapordeposition) method as shown in FIG. 7, and a protective film 4 is formedfor its protection.

In greater detail, coating by vapor deposition is performed in a vacuumin the same way as the vacuum deposition of metal, and includes a stepof subjecting a diparaxylylene monomer used as a raw material to thermaldecomposition, then quickly cooling a resulting product in an organicsolvent such as toluene or benzene, and obtaining diparaxylylene whichis called dimer, a step of subjecting this dimer to thermaldecomposition and gathering a stable radical paraxylylene gas, and astep of causing the thus generated gas to be absorbed and polymerizedonto a material so as to form a polyparaxylylene film having a molecularweight of about 500,000 by polymerization.

There is a gap between the columnar crystals of CsI, and Parylene entersthis narrow gap to some extent, so that the protective film 4 comes infirm contact with the layer of the scintillator 3 and seals up thescintillator 3. The Parylene coating makes it possible to form a precisethin-film coating, which is uniform in thickness, on the uneven layersurface of the scintillator 3. Under the CVD method, Parylene can beformed at a lower vacuum degree than in metal deposition and at normaltemperatures, and can be easily processed.

The protective film 4 formed subsequently to this is slit between theelectrode pad 23 and the shift register 24 and along the outside of thesidewall 25, and the outer protective film 4 is peeled off. Thereby, theelectrode pad 23 is exposed, and an image sensor panel shown in FIG. 8is obtained.

Thereafter, a UV cured resin, for example, of 10 to 20 μm in thicknesscontaining divinylbenzene is applied to the sidewalls 25 of thesolid-state image sensing devices 2 a to 2 d thus formed as image sensorpanels on the flat surface of the base 1 so that the sidewalls 25 buttagainst each other, and the cured resin is hardened in the 2×2 array ofthe image sensing devices with the light receiving surface of thephotoelectric detector 21 as an upper face so as to dispose theelectrode pads 23 outside while the light receiving sections 22 areadjacent to each other, whereby the image sensing devices 2 a to 2 d arebonded together and are fixed to the base 1. As a result, the radiationdetector 100 shown in FIG. 1 is obtained. A circuit section electricallyconnected to the photoelectric detectors 21 and a bonding pad areprovided between at least one of the other sides that are not adjacentto the light receiving section 22 of the image sensor panel and thelight receiving section 22.

Next, the operation of this embodiment will be described with referenceto FIG. 1 and FIG. 2. X rays (radiation) that have entered from anincidence surface pass through the protective film 4, and reach thescintillator 3. The X rays are absorbed by the scintillator 3, and lightof a predetermined wavelength proportional to the quantity of the X raysis emitted. The emitted light reaches the photoelectric detectors 21 inthe light receiving section 22. In each photoelectric detector 21, anelectrical signal corresponding to the quantity of the light that hasreached it is generated by a photoelectric conversion, and is stored fora fixed time. Since the quantity of the light is proportional to thequantity of the incident X rays, the electrical signal stored in eachphotoelectric detector 21 corresponds to the quantity of the incident Xrays, and an image signal corresponding to an X-ray image can beobtained. The image signals stored in the photoelectric detectors 21 aresuccessively output from each electrode pad 23 through the shiftregister 24 from a signal line not shown, are then transferred outward,and are processed by a predetermined processing circuit, whereby anX-ray image can be displayed on a monitor.

The solid-state image sensing device 2 that is an image sensor panelaccording to the present invention has a uniform layer of thescintillator 3 extending to the edge of the light receiving section 22.Additionally, the light receiving sections of the solid-state imagesensing devices 2 can be disposed adjacent to each other, and thereforea dead space that is an insensible field between the solid-state imagesensing devices 2 can be controlled to the width of one to three pixels,and effective use can be made to the edge of the light receiving section22.

In contrast, if the scintillator 3 is formed on the solid-state imagesensing device 2 by use of the vapor-deposition-substrate holders 210and 220 shown in FIG. 9 and FIG. 10, the scintillator 3 cannot besufficiently formed at the edge of the light receiving section 22 asshown in FIG. 11 or FIG. 12. Therefore, in spite of the fact that thesolid-state image sensing devices 2 are disposed as close to each otheras possible, a dead space is inevitably generated between thesolid-state image sensing devices 2, and, in addition, the layer of thescintillator 3 is insufficient. Therefore, an area that cannot obtain asufficient quantity of light arises to the extent of several pixels totens of pixels, and an unnegligible dead space (insensible field) willbe generated. According to the present invention, the width of such aninsensible field can be made small enough to be negligible.

Further, according to the present invention, since the protective film 4extends to the sidewall 25, and, in addition, the sidewall 25 is fixedwith resins, the scintillator 4 can be effectively prevented fromseparating, and its durability can be secured. Further, since detectorswith a small light receiving screen are combined together, the yield foreach component can be prevented from decreasing greater than a casewhere large-screen detectors are manufactured, and production costs canbe reduced.

FIG. 13 is a plan view showing a second embodiment of the radiationdetector according to the present invention. As shown in this figure,the solid-state image sensing devices 2 a and 2 b that are two imagesensor panels may be coupled together to manufacture a radiationdetector with a large screen. Further, it is allowable to arrange threeor more solid-state image sensing devices in a row so as to make a largescreen or arrange them in 2×m array or in m×n array for a large screen.If the solid-state image sensing devices are arranged in 2×m array(where m is 3 or an integer greater than 3), solid-state image sensingdevices 2′ other than the image sensing device disposed at at least fourcorners are required to have a structure (see FIG. 14) in which thelight receiving section 22 is disposed up to the boundary of at leastthree sides. If the solid-state image sensing devices are arranged inm×n array (where m and n are each 3 or an integer greater than 3),solid-state image sensing devices 2″ disposed at the inner partexcluding the peripheral part are required to have a structure (see FIG.15) in which the light receiving section 22 is disposed on the entiresurface. In this case, it is preferable to dispose the electrode pad onthe back face and read a signal by the use of a wire passing through thebase 1. It is, of course, obvious that each of the aforementionedsolid-state image sensing devices can be used as an individual detector.

FIG. 16 is a sectional view showing a third embodiment of the radiationdetector according to the present invention. Scintillator panels 6 a and6 b according to the present invention are disposed on the solid-stateimage sensing devices 2. In each scintillator panel 6, the scintillator3 successively extends from one side face 61 of a glass board 60, whichserves as a scintillator-forming substrate, toward the sidewall 62, anda protective film 4 of Parylene is formed so as to cover and wrap thescintillator 3. The scintillator panels 6 a and 6 b are disposed on thelight receiving section 22 of one solid-state image sensing device 2 ina state where the sidewalls 62 butt against each other, and a side wherethe scintillator 3 is formed is directed to the solid-state imagesensing device 2.

Since a method for manufacturing the scintillator panel 6 follows thesteps shown in FIG. 4 to FIG. 8, a description thereof is omitted. Whenthis scintillator panel 6 is used, the same effect as the radiationdetector of the first embodiment can be obtained. Not only on the sideof the scintillator panel 6 but also on the side of the solid-stateimage sensing device 2, a plurality of solid-state image sensing devicesmay be combined like a panel. If the scintillator side of thescintillator panel is directed to the light receiving section of thesolid-state image sensing device, the board 60 forming the scintillatorneeds to be radiolucent. Al- or Be made board, instead of glass, or amaterial mainly composed of carbon, such as amorphous carbon orgraphite, can be used as a radiolucent board.

If the side of the board 60 of the scintillator panel is directed to thelight receiving section of the solid-state image sensing device, theboard needs to be transmissible to light emitted from the scintillator,and glass to be penetrated by visible light is preferred when CsI isused as the scintillator.

In the foregoing description, the protective film 4 is a Parylene-madeprotective film having a single film structure. However if a reflectionfilm that is a thin surface of the Parylene-made film in the first andsecond embodiments, an image with high brightness can be obtained byreturning the light emitted from the scintillator 3 to the photoelectricdetector 21. Further, in the third embodiment, an image with highaccuracy can be obtained by providing a reflection film between theradiolucent board and the scintillator. In the first and secondembodiments, a Parylene film, for example, may be applied onto thesurface of the metallic thin film for the protection of the metallicone. When a moisture-proof material is used as the scintillator 3 orwhen the whole of the device is contained in a moisture-proof protectivecase, the protective film 4 is not needed.

INDUSTRIAL APPLICABILITY

The radiation detector and the scintillator panel according to thepresent invention can be suitably used as a radiation detector and ascintillator panel to get a radiation image having a large area.

1. A radiation detector comprising: an image sensor panel having asubstrate and a light receiving section consisting of a plurality ofdetectors two-dimensionally arranged in the vicinity of at least oneside on the substrate, and a scintillator formed by vapor depositionfrom a surface of the light receiving section of the image sensor panelto a sidewall part in the vicinity thereof wherein the image sensorpanel is provided in a plurality, and each of the image sensor panels isfixed by disposing sidewalls where the scintillator is formed so as tobe adjacent to each other, and wherein resulting scintillator portionsfor each image sensor panel are respectively covered with amoisture-proof protective film.
 2. A scintillator panel comprising: ascintillator-forming substrate, and a scintillator formed by vapordeposition from a sidewall part of at least one side of thescintillator-forming substrate to a predetermined area of one surface ofthe scintillator-forming substrate wherein the scintillator-formingsubstrate is provided in a plurality, and, sidewalls where thescintillator of each of the scintillator-forming substrates is formedare disposed and fixed to be adjacent to each other, and whereinresulting scintillator portions for each scintillator-forming substrateare respectively covered with a moisture-proof protective film.
 3. Thescintillator panel according to claim 2, wherein thescintillator-forming substrate is radiolucent.
 4. A radiation detectorcomprising: the scintillator panel according to claim 2, and an imagesensor panel in which a light receiving section formed bytwo-dimensionally arranging photoelectric detectors is disposed to facesaid scintillator.
 5. A method for manufacturing a radiation detector,the method comprising steps of: preparing one or more image sensorpanels each of which has a light receiving section in which a pluralityof photoelectric detectors are two-dimensionally arranged in thevicinity of at least one side of a substrate, and forming a scintillatorby vapor deposition from a surface of the light receiving section ofeach of the image sensor panels to a sidewall part close to the lightreceiving section further comprising a step of fixing the plurality ofimage sensor panels obtained after the scintillator is formed by causingsidewalls where the scintillator is formed to be adjacent to each other.6. The method for manufacturing the radiation detector according toclaim 5, further comprising a step of covering the scintillator with amoisture-proof protective film after the scintillator is formed.
 7. Amethod for manufacturing a scintillator panel comprising steps of:preparing one or more scintillator-forming substrates, and forming ascintillator by vapor deposition from a sidewall part of at least oneside of the scintillator-forming substrate to a predetermined positionof a surface of the substrate further comprising a step of fixing theplural scintillator-forming substrates obtained after the scintillatoris formed by causing sidewalls where the scintillator is formed to beadjacent to each other.
 8. The method for manufacturing the scintillatorpanel according to claim 7, further comprising a step of covering thescintillator with a moisture-proof protective film after thescintillator is formed.
 9. A method for manufacturing a radiationdetector comprising a step of disposing and fixing a light-receivingsurface of a solid-state image sensing device so as to face ascintillator of a scintillator panel manufactured by the methodaccording to any one of claims 7 to 8.